This invention relates generally to electrostatographic reproduction machines, and more particularly to a non-interactive, low-friction single component developer material development apparatus that enables use of fragile and easily fused toners without toner degradation. The present invention can be utilized in the art of xerography or in the printing arts.
The art or process of xerography involves forming electrostatic latent images on a surface by first uniformly charging a photoreceptor. The photoreceptor comprises a charge retentive surface. The charge is image-wise selectively dissipated in accordance with an image pattern of activating radiation corresponding to an original image. The selective dissipation of the charge leaves a latent charge pattern on the imaging surface corresponding to the areas not exposed by radiation.
This charge pattern is then developed, or made visible with a development apparatus or unit containing developer material such as single component, or toner and other components including carrier particles. The toner is generally a colored powder which is charged and adheres to the charge pattern by electrostatic attraction resulting in a toner developed image. The toner developed image is then fixed to the imaging surface or is transferred to a receiving substrate such as plain paper to which it is thereafter fixed by suitable fusing techniques.
Black and white toner images can be formed by the process as described above, and multicolor toner images can be similarly formed by using not just one but several development units containing different colors of toner. Such multicolor toner images can be highlight color images or full color images. One approach for forming such toner images is in a single pass of the photoreceptor during which color separation toner images are formed in registration, one on another, or in what is called an "image-on-image" manner.
The viability of image-on-image reproduction machines, such as those for producing highlight color or image-on-image full color images, requires development units that are non-interactive, i.e. developments units that do not scavenge or interact with a previously toned image on the photoreceptor. Although development units and techniques have been proposed for achieving non-interactive or scavengeless development, developer material degradation or the need to use hard-to-fuse toner continue to present problems with most such development units.
This is so because on the one hand, in order to enable efficient electrostatic transfer of xerographic toner images from a photoreceptor to plain paper, the toner should be insulating so as to prevent charge reversal at the toner-paper interface. The method commonly used for charging such insulating toner involves the phenomenon of triboelectricity which requires high-frictional contacts between the toner and other materials such as carrier beads in two-component developer systems, or metering blades, rods and donor rolls, in single component developer systems. On the other hand however, such required high frictional contacts tend to cause undesirable premature developer material or toner degradation.
It has been found that in order to prevent such undesirable material degradation so as to achieve and maintain stable system performance, mechanical stresses involved in the toner triboelectric charging process as above, must not exceed the toner yield stress. Additionally, from a toner fusing standpoint, toners that flow well under the application of heat and/or pressure are of course preferred. This is particularly desired for color imaging where low-melt toners are preferred. For these reasons, toners that tend to be fragile are strongly preferred. Unfortunately, they cannot withstand the high frictional contacts required by triboelectric charging, and there is therefore a need for low-friction single component development systems that are gentle on such toners.